Osteoporosis is a major health problem. Optimum development of the skeleton during youth is crucial in prevention of osteoporosis, a condition that fractures bone late in life because of reduced bone mass and bone quality. If skeletal development can be maximized during growth, young people will begin adulthood with optimal bone health and be less likely to develop osteoporosis in later years. Yet bone health in youth has not been adequately addressed. In this application, we propose to extend our four-year intervention study of the effects of a high calcium diet on bone quality in pubertal girls. The aim of this experimental study is to test the effect of increasing dietary calcium intake to 1500 mg/day on increases in bone quality in adolescent females. The hypothesis to be tested is: adolescent females who consume a high calcium diet will have a greater increase in bone quality, as measured by densitometry and ultrasound, then adolescent females who consume their usual dietary calcium intake. The study uses an experimental design in which 58 participants (26 treatment and 32 control) will be followed for an additional 4.5 years for a total of 8.5 years. Participants are a convenience sample who were age 9 when enrolled. Girls in the treatment group will continue to be given high calcium foods to supply at least 1500 mg/day while girls in the control group will be asked to continue consuming their usual diet. Measurements to be made at baseline, every six months, and at the end of the study include height, weight, Tanner stage, and medical and social history. Usual physical activity and dietary intake will be determined every three months. Funding of this project in the next cycle would enable us to follow these young females continuously from age 9 to age 18.5. To our knowledge, this would be the first intervention to evaluate the effects of optimal calcium intake on bone health through out the period of highest bone mass and bone quality accrual. This enthusiastic group of adolescent participants provides us with confidence that we can successfully complete this ambitious project. Evidence of a positive effect of increased calcium intake from food sources on bone quality in adolescent females would provide strong support for educational efforts targeted at adolescent females, parents and care providers. Negative findings would provide support for further research into other methods of concomitant methods of maximizing skeletal development.